Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
To ensure accurate color reproduction, there is proposed a technique that prints color patches, detects the printed color patches by a sensor, and then calibrates an image formation process. As a technique related to this, there is proposed a technique that uses a ladder patch as a color patch. The ladder patch has a plurality of thin, line-shaped patches, which are adjacently arranged. Assuming that print densities of respective straight-line portions of the ladder patch are identical to the print density of a solid patch, the technique enables detection in a print density region (a region with a large reflection-light amount by a combination with a background portion) where a detection sensitivity of an optical sensor is high. On the other hand, there is also proposed a technique that reduces generation of a transfer scattering (diffusion of toner to an outside of an image range) caused by edge effect, by reducing toner attachment amount in a contour portion of a toner image due to image processing or an adjustment of a gap.